<!DOCTYPE html>
<style>
#mask {
  width: 200px;
  height: 200px;
  overflow: hidden;
  border-radius: 10px;
  border: 4px solid red;
  background-color: grey;
  position: absolute;
}

.scale-seam {
  transform-origin: 0 0;
  transform: scale(2, 1);
  display: inline-block;
  position: absolute;
}

.content {
  width: 500px;
  height: 500px;
  position: absolute;
}

.composited {
  will-change: transform;
}
</style>

<p>Testing masks on compositing layers. Top and bottom rows should look the same.</p>
<div class="scale-seam">
  <div id="mask">
    <div class="content" style="left: 0;top: 0;background: black;position: absolute;"></div>
  </div>
</div>

<div class="scale-seam" style="top: 300px;">
  <div id="mask" class="composited">
    <div class="content" style="left: 0;top: 0;background: black;position: absolute;"></div>
  </div>
</div>
